Field of the Invention
Embodiments of this disclosure generally relate to valves for use in downhole pumps.
Description of the Related Art
Pumps can be used in wells to help bring production fluids to the surface. This is often referred to as providing artificial lift, as the reservoir pressure is insufficient for the production fluid to reach the surface on its own.
One type of pump for such operations is a hydraulically-actuated piston pump, such as the pump disclosed in U.S. Pat. No. 8,303,272, incorporated herein by reference. This type of pump is typically deployed downhole in tubing disposed in a wellbore casing. Surface equipment injects power fluid (e.g., produced water or oil) down the tubing to the pump. The power fluid operates to drive an engine piston internally between upstrokes and downstrokes which, in turn, drives a pump piston connected to the engine piston via a rod.
In its upstroke, the pump draws in production fluid to a lower (intake) pump volume below the pump piston. In its downstroke, the pump transfers the production fluid from the lower pump volume to an upper (discharge) pump volume above the pump piston. In a subsequent upstroke, the production fluid and “spent” power fluid (that was used to drive the engine piston) is discharged from the discharge volume via the tubing-casing annulus (or some such parallel path) to the surface equipment for handling.
Hydraulic piston pumps often utilize check valves, such as those shown in FIG. 1, that utilize small balls to prevent back flow within the pump. Assuming a pump that operates in a manner described above, a first check valve 10 may allow flow of the production fluid from the lower pump volume to the upper pump volume on a downstroke as the lower pump volume decreases and pressure in an inlet port 12 rises to a sufficient level to unseat ball 14 (biased in a seated position by spring 16). The check valve 10 prevents back flow of the production fluid to the lower pump volume during the upstroke, as pressure at the port 12 falls with increasing lower pump volume and the ball 14 re-seats.
A second check valve 20 may allow discharge of the production and spent power fluid on an upstroke as the upper pump volume decreases and pressure in an inlet port 22 rises to a sufficient level to unseat ball 24 (biased in a seated position by spring 26). The second check valve 20 also prevents flow of fluid back into the pump on the downstroke, as pressure at the port 22 decreases and ball 24 re-seats.
Unfortunately, balls used in conventional check valves such as these can damage the seat when high volumes of gas are required to pass through the pump. Additionally, debris can lodge between the ball and seat and cause excess leakage in the pump. When the pump stops operating due to the balls sticking open or when the balls damage the valve plate, the pump is typically removed from the well, resulting in substantial repair costs and operating down time.
Therefore, what is needed is an improved check valve assembly that addresses these shortcomings.